The present invention relates to gel electrophoresis. More particularly, this invention relates to methods, articles and kits for labeling polymer gels used for gel electrophoresis.
Gel electrophoresis is among the most common analytical procedures used in biologic research, and is used to characterize, separate, and at times to purify a wide variety of biological molecules, including deoxyribonucleic acid (xe2x80x9cDNAxe2x80x9d), ribonucleic acid (xe2x80x9cRNAxe2x80x9d) and proteins.
The basic principles are well established. A gel, such as polyacrylamide or agarose, is first solidified from a liquid solution by polymerization within a rigid gel casting form. To effect separation of an analytical mixture, an electric potential is applied across the length of the polymer gel, either as enclosed within the casting form or, particularly in the case of agarose gels, after removal of the gel from the casting form. Charged analytes placed within the gel are then separated and distinguished from one another based upon their differential mobility through the gel matrix under the motivating influence of the applied electric field.
Researchers either prepare their own gels or purchase them precast from commercial suppliers. Frequently, large numbers of gels are prepared and run. Where such gels are of identical dimension, it is critical that the gels be distinguished from one another so that results of various experiments are not confused with one another and the results misinterpreted.
However, it is difficult to mark the gel surface (e.g., by writing on the gel), and the gel shape may not easily be modified without disturbing the uniformity of the electric field desired to be maintained in the gel during electrophoresis. Although the gel cassette in which the electrophoresis may have been conducted can readily be labeled, such a label does not remain with the gel once the gel is removed for staining or further processing.
Furthermore, it is frequently difficult after electrophoresis to determine the orientation that the gel had maintained during electrophoresis. For example, the researcher may be unable readily to determine after electrophoresis which side of the gel had been proximal to the anode and which proximal to the cathode, particularly if the sample wells have been removed from the gel.
One known technique for labeling and orienting polymer gels is to remove the gel from its enclosing cassette after performing electrophoresis, and then notch or cut one of the gel""s four corners. This technique, however, does not provide an identification mark that is visible both prior to and following electrophoresis. Nor does this technique provide unambiguous identification, especially when several gels are being stained or processed simultaneously. And because the gels have at most four corners that may be notched, this technique allows at most four gels to be identified at a time.
Another previously known technique for labeling gels is to include within the gel a piece of filter paper that contains identifying marks, such as written or printed characters. This technique, however, causes both physical and optical problems.
The filter paper can, for example, cause localized disturbance in the electric field, either directly, or indirectly through a local change in temperature or electrolyte concentration, thus distorting the migration of analytes through gel. The paper, although physically entrapped in the gel, may still separate therefrom, or may weaken the gel so that the gel breaks easily, allowing the label to come free.
The filter""s opacity may obscure detection of analyte in portions of the gel that it overlies. Furthermore, following electrophoresis, the filter paper may take up the stains that are used to render the analytes themselves detectable, further obscuring the analytes in the gel. It goes without saying that the filter is unsightly.
Transparent films have been described that are useful for imparting structural rigidity to polymer gels used in gel electrophoresis. The films, when placed in contact with the gel during polymerization, bond irreversibly to the polymerized gel, either by covalent or strong noncovalent bonds. These films, available commercially, have not been taught to be useful if smaller in surface area than the gel to be supported thereon. Such films have also not been taught to be useful substrates for applying indicia that would serve unambiguously to identify the adherent gel.
It would be desirable to provide improved methods, articles and kits for labeling polymer gels used for gel electrophoresis.
It would further be desirable to provide methods, articles and kits for labeling gels whereby the label does not interfere with electrophoresis or with post-electrophoresis processing and does not easily separate from the gel.
It would also be desirable to provide methods, articles and kits for labeling polymer gels used for gel electrophoresis whereby the label has an aesthetically pleasing appearance and where the label""s substrate is, preferably, substantially transparent.
These and other objects are solved by the present invention, which provides novel methods, articles, and kits for labeling polymer gels used for gel electrophoresis.
In a first aspect, the invention provides methods for detectably labeling a polymer gel, comprising bonding a polymeric film to the gel during gel polymerization. The polymeric film has indicia that are detectable after the film is so bonded, thereby permanently labeling the gel.
In another aspect, the invention provides labeling articles for use in the aforesaid methods. The article comprises a polymeric film having detectable indicia, and, optionally, a coating. When the coating is absent, the polymeric film is itself capable of bonding to the polymeric gel during its polymerization. When the coating is present, the coating is capable of bonding the polymeric film to the gel during polymerization. In either case, the indicia are detectable after the film is so bonded.
The methods and articles of the present invention are useful with polymer gels of a wide variety of compositions, including polyacrylamide, agarose, and derivatives thereof.
In a typical embodiment, the polymeric film is a polyester with a single layer coating of hydrophilic resin with ethylenically unsaturated groups, or a polyester film with a two-layer coating wherein the first layer is a vinyl acetate-maleic acid copolymer in direct contact with the film, and the second layer is a layer of dried agarose.
Often, the indicia will be detectable both before and after electrophoresis, either by epiillumination, transillumination, or both. In some embodiments, the indicia will be detectable using natural light for illumination; in other embodiments, the indicia are detectable only after illumination with nonvisible wavelengths.
In another aspect, the invention provides pre-cast polymer gels labeled with detectable indicia, comprising: a polymer gel; and a polymeric film having detectable indicia, wherein the polymeric film is bonded to the polymer gel and the indicia are detectable with the film so bonded.
The invention further provides a kit for labeling a polymer gel, comprising: at least one labeling article packaged in association with instructions for bonding the label to a polymer gel during gel polymerization.